The rapidly growing market for electronics has led to a great demand for electrically conductive polymers. Electronic devices generate radio frequency radiation during operation, and to prevent consequent electromagnetic interference (EMI) with other devices, it is necessary to shield the source with an electrically conductive material. Polyamide resins are characterized by excellent mechanical properties, moldability, and chemical resistance and have, therefore, been used in automotive parts, mechanical components, and many other applications. Polyamides have also been used in electrical and electronic applications but, used alone, they are not electrically conductive and do not provide the EMI shielding and low warpage properties that are required for applications such as computer housings.
Polyamide resin compositions suitable for use in applications where EMI shielding is required are known. For example, the use of mixtures of thermoplastic resins, conductive fibers, and 20 weight percent of thermosetting resins such as a phenolic resin is disclosed in Japanese laid open patent 09-87417 (1997), and a blend of mixtures of two different thermoplastic resins and conductive fibers is disclosed in Japanese laid open patent 11-255907 (1999). No mention is made of any improved moisture absorption, warpage, and dimensional stability properties possessed by these resins.
There is still a need for a polyamide resin compositions that can be molded into objects that possess excellent EMI shielding characteristics as well as low levels of warpage and good dimensional stability. It is therefore an object of the present in invention to provide a composition that possesses these qualities. A feature of the present invention is that compositions disclosed herein are capable of being formed into articles that possess excellent EMI shielding characteristics as well as low levels of warpage and moisture absorption, which leads to good dimensional stability. An advantage of the present invention is that these compositions may be used to manufacture articles for applications where both EMI shielding performance and low levels of warpage and dimensional stability are required. These and other objects, features and advantages of the invention will become better understood upon having reference to the description of the invention herein.